7. Diabeties Clinical Cases

Question 1

High pH, low PCO2?

Answer 1

respiratory alkalosis

Question 2

When is an anion gap seen?

Answer 2

DKA

Question 3

Formula for anion gap?

Answer 3

Na + K - Cl - bicarbonate

Question 4

High pH, high pCO2?

Answer 4

metabolic alkalosis

Question 5

Low pH, low pCO2?

Answer 5

metabolic acidosis

Question 6

Low pH, high pCO2

Answer 6

respiratory acidosis

Question 7

Osmolality equation

Answer 7

2(Na + K) + Urea + Glucose

Question 8

Large anion gap (excess anions), no ketones, metabolic acidosis. What is the cause?

Answer 8

High anion gap is suggestive of some other form of tocin in patients blood. Methanol, ethanol, lactate. Metformin overdose? Ketones, ethylene glycol.

Question 9

Definition of Type 2 diabetes?

Answer 9

• Fasting glucose > 7.0mM
• Glucose tolerance test (75 grams glucose at time 0)
• Plasma glucose > 11.1 mM at 2 hours
• (2h value 7.8 - 11.1 = impaired glucose tolerance)

Question 10

Case 1

16 year old unconscious. Acutely unwell a few days. Vomiting. Breathless.
pH 6.85, PCO2 = 2.3 kPa (N 4-5), PO2 = 15 kPa

Interpret.

Answer 10

• This is metabolic acidosis as pH is low so there is an excess of H+ ions and CO2 is low (and bicarbonate is low according to equilibrium)
• equilibrium equation: HCO3- + H+ = CO2 + H2O
• The patient is unconscious as brain enzymes cannot function at acidic pH

Question 11

Case 2

A 19 year old known to have type 1 diabetes for several years presents unconscious
Results: pH 7.65, pCO2 = 2.8 kPa, Bicarb = 24 mM (normal), pO2 = 15 kPa

Interpret.

Answer 11

This is respiratory alkalosis as pH is high and CO2 is low. Probably due to primary hyperventilation – anxiety caused by hypoglycaemia.

When the pH increases the plasma proteins start to stick to calcium more than usual, so the plasma calcium appears normal however there will be less free ionised calcium

• A fall in free ionised calcium will result in tetany which can make the patients hyperventilate more
• The treatment is to get them to calm down e.g. breath into a brown paper bag – this doesn’t do anything but distract the patient by getting them to focus on their breathing
• Anion gap = (140 + 4.0) – (100 + 24) = 20 = normal

Question 12

Why does the patient with respiratory alkalosis hyperventilate? What can be done immediately?

Answer 12

Anxiety caused by hypoglycaemia, causes hyperventilation. When pH increases, plasma proteins start to ctick to calcium more, so plasma calcium seems normal but less free calcium. Fall in free calcium leads to tetany, making patients hyperventilate.

The treatment is to get them to calm down e.g. breath into a brown paper bag – this doesn’t do anything but distract the patient by getting them to focus on their breathing

Question 13

Case 3

Case 3

60 year old man presents unconscious to casualty, with a history of polyuria and polydipsia.
Investigations reveal: Na: 160, K: 6.0, U 50, pH 7.30, Glucose 60.

What is the osmolality?

Answer 13

Osmolality = 2(160 + 6.0) + 50 + 60 = 442 mmol/L.

Question 14

Case 3

60 year old man presents unconscious to casualty, with a history of polyuria and polydipsia.
Investigations reveal: Na: 160, K: 6.0, U 50, pH 7.30, Glucose 60.

Osmolality is high, what does this mean?

Answer 14

The patient becomes unconscious as the brain is very dehydrated. This is hyperosmolar hyperglycaemic state (HHS).

Question 15

Case 3

Case 3

60 year old man presents unconscious to casualty, with a history of polyuria and polydipsia.
Investigations reveal: Na: 160, K: 6.0, U 50, pH 7.30, Glucose 60.

Patient is in a hyperosmolar hyperglycaemic state. Why should you not give lots of fluid and what should you do?

Answer 15

If you give them lots of fluid and try to normalise the numbers too quickly they will get cerebral oedema and die so they need to be treated cautiously and slowly. You should use 0.9% saline because this will enable a slower reduction in plasma sodium concentration.

Question 16

Case 4

59 year old man known to have type 2 diabetes, on a good diet and metformin presents to casualty unconscious
Urine is negative for ketones.
Na: 140, K: 4.0, U 4.0, pH 7.10, Glucose 4.0, PCO2=1.3 kPa. Cl = 90. Bicarb = 4.0 mM
Lactate = 10mM (N<2.0)

Interpret (include acid-base balance, osmolality, anion gap, potential causes?)

Answer 16

This is metabolic acidosis as pH is low and CO2 is low. Osmolality = 2(140 + 4.0) + 4.0 + 4.0 = 296 mmol/L. Anion gap = (140 + 4.0) – (90 + 4.0) = 50 = high. There are no ketones so there must be some other acid involved e.g. methanol, ethanol, lactate (also excess lactic acid caused by metformin overdose).

Question 17

How can a metformin overdose cause lactic acidosis, thus causing metabolic acidosis?

Answer 17

Cori cycle:
This is the metabolic pathway by which lactate is produced by anaerobic glycolysis in the muscles and moves to the liver to be converted to glucose, which then returns to the muscles and is metabolised back to lactate.
Metformin can cause lactic acidosis because it inhibits hepatic gluconeogenesis
Normally, excess lactate will be cleared by the kidneys, but in patients with renal failure, the kidneys cannot handle the excess lactic acid.

Question 18

What is type 2 diabetes defined as?

Answer 18

1. Fasting glucose > 7.0 mM
2. Oral glucose tolerance test where 75g of glucose is given at t = 0. Diabetes -> plasma glucose >11.1 mM at 2 hrs.
   NOTE: plasma glucose is different to whole blood glucose

Question 19

What acid-base imbalance does COPD lead to and how?

Answer 19

COPD leads to the development of chronic respiratory acidosis. In COPD the lungs slowly fail and pCO2 increases gradually, as this happens you become very breathless as CO2 is potent respiratory stimulus (hypercapnic drive)

Question 20

Why do pink puffers present the way they do and how do they turn into blue bloaters?

Answer 20

Pink puffers are very breathless as they are still sensitive to the raised CO2. There will eventually become a point when your brain has had enough of this raised CO2 state and will stop being as responsive to CO2 🡪 CO2 no longer becomes a driver to breathe. This makes you a blue bloater, you are not breathless but your CO2 will continue to rise. The kidneys will try and compensate by retaining HCO3.